1. Field of the Invention
The field of this invention relates to polyamides prepared from itaconic acid and diamines. These novel polyamides are useful in preparing molded articles, fibers, laminates and coatings.
2. Background
It is known to make polyamide-imides from trimellitic anhydride chloride and aliphatic or aromatic diamines in polar solvents. (See U.S. Pat. Nos. 3,661,832 and 3,260,691.) The hydrochloric acid produced in this process is removed by precipitation of the polymer in a precipitant such as water. Alternatively, U.S. Pat. No. 3,347,828 shows that the hydrochloric acid may be neutralized by adding alkaline oxides. British Patent Specification 570,858 discloses various processes for making fiber forming polyamides. In reviewing the references, it is clear the use of itaconic acid to form polyamides useful as moldings, fibers, laminates, and coatings has not been contemplated in the prior art.
The general object of this invention is to provide novel polyamides based on itaconic acid and diamine moieties. A more specific object of this invention is to provide polyamides from itaconic acid moieties and aliphatic, cycloaliphatic, araliphatic and aromatic moieties. Another object is to provide a process for the manufacture of polyamides, from itaconic acid and diamines.
We have found that novel polyamides can be formed by reacting itaconic acid with diamines. Itaconic acid reacts readily with the diamine to form a pyrrolidone which polycondenses to a high molecular weight polyamide. In the novel process both aliphatic and aromatic diamines can be polymerized with itaconic acid in the melt to form high molecular weight polyamides.
Our process for the manufacture of the novel polyamides comprises reacting about equal molar amounts of itaconic acid with a primary diamine or a mixture of primary diamines. The molecular ratio of the itaconic acid to the primary diamine may be in the range of 0.95 to 1.10, preferably in the range of 0.98 to 1.05. In the preferred method, the reaction is carried out under pressure in the presence of water to facilitate the formation of the pyrrolidone. The water is then distilled and the temperature is raised from about 150.degree. F. to 525.degree. F. to complete the polycondensation. The polycondensation can suitably be carried out at a temperature of 475.degree. F. to 550.degree. F., preferably at a temperature of 500.degree. to 525.degree. F. The order of addition of the reactants is not critical and all the reactants can be added simultaneously in any order desired. The novel polyamides of this invention have the following recurring structure wherein R is a divalent aliphatic or aromatic hydrocarbon radical. ##STR1## The radical R may be a divalent aliphatic hydrocarbon of 2 to 18 carbon atoms or an aromatic hydrocarbon from 6 to 20 carbon atoms, or an aromatic hydrocarbon radical containing from 6 to 10 carbon atoms joined directly or by stable linkage comprising --O--, methylene, ##STR2## radicals. The radical R is derived from aliphatic, araliphatic or cycloaliphatic diamines such as ethylenediamine, propylenediamine, 2,2-dimethylpropylene diamine, tetramethylene diamine, hexamethylene diamine, octamethylene diamine, nonamethylene diamine, decamethylene diamine, dodecamethylenediamine, 4,4'-diaminodicyclohexylmethane, xylylene diamine and bis (aminomethyl) cyclohexane. Suitable aromatic diamines useful in applicant's process include para- and meta-phenylenediamine, oxybis (aniline), thiobis (aniline), sulfonylbis (aniline), diaminobenzophenone, methylenebis (aniline), benzidine, 1,5-diaminonaphthalene, oxybis (2-methylaniline), thiobis (2-methylaniline), and the like. Examples of other useful aromatic primary diamines are set out in U.S. Pat. Nos. 3,494,890 (1970) and U.S. Pat. No. 4,016,140 (1972) both incorporated herein by reference.
In some cases the polyamide may be further polymerized under "solid state polymerization" conditions. The term solid state polymerization refers to chain extensions of polymer particles under conditions where the polymer particles retain their solid form and do not become a fluid mass. The solid state polymerization can be carried out below the melting point of the polyamide and can be conducted in several ways. However all techniques require heating the ground or pelletized polyamide below the melting point of the polyamide, generally at a temperature of about 180.degree. C. to 225.degree. C. while either sparging with an inert gas such as nitrogen or air or operating under vacuum. In cases where the polyamides have a low melt temperature, they can be polymerized in the melt under vacuum in thin sections or using thin film reactors known in the art.
Injection molding of the novel polyamide is accompanied by injecting the polyamide into a mold maintained at a temperature of about 45.degree. F. to 300.degree. F. In this process a 20 second to 1 minute cycle is used with a barrel temperature of about 450.degree. F. to 600.degree. F. The latter will vary depending on the T.sub.g of the polymer being molded.
The novel polyamides have excellent mechanical and thermal properties and can readily be molded, formed into fibers, films, laminates or coatings. The tensile properties of the polyamides made with several diamines are shown on Table I. Tensile strength of 7,000 to 12,000 psi indicates that high molecular weight polyamides are formed. Infrared spectra of the polyamides has confirmed the polyamide structure and also shows the absence of any imide structure or unsaturation in the polyamides. Carbonyl band heights are also consistent with two types of amide groups in the polyamide, the two types are secondary and tertiary amide groups. Characteristic absorption bands are shown in Example I for the itaconic acid/hexamethylene diamine polymer.
Thermal analysis of the hexamethylenediamine itaconic acid polyamide by thermal gravimetric analysis shows excellent stability. This is demonstrated by the fact that under nitrogen atmosphere the main weight loss occurs at a temperature of 330.degree. centigrade and 1% additional weight loss occurs at a temperature of about 397.degree. centigrade. Glass temperature (T.sub.g) of the polyamide varied with the particular diamine used as shown in Table I. Values range from a T.sub.g of 22.degree. C. for a polyamide prepared from dodecanediamine and itaconic acid and increase to 128.degree. and 160.degree. centigrade for polyamides made from itaconic acid and m-bis(aminomethyl)cyclohexane, and m-xylylenediamine.
Diamines with the amino groups attached directly to the aromatic ring are suitably polymerized with itaconic acid by solution condensation in organic polar solvents. Useful polar solvents include N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, dimethylsulfoxide and the like. Polyamides made from itaconic acid and aliphatic diamines show high moisture pick up. Sometimes up to seventy-five percent of weight of these polyamides is increased by moisture pick up. The polyamides are useful in fiber applications to modify nylon 6,6 by copolymer formation.
The itaconic acid polyamide can be used to prepare copolyamides containing about 2-70% of the itaconic acid polyamide and the remainder being dibasic acids or lactams as comonomers. Suitable dibasic acids are adipic acid and related aliphatic acids. Suitable lactams are caprolactam, etc.
The following examples illustrate the preferred embodiment of the invention. It will be understood that the examples are for illustrative purposes only and do not purport to be wholly definitive with respect to conditions or scope of the invention.